1. Field of the Invention
The present invention relates to a wheel suspension system for a steerable wheel, and in particular to a wheel suspension system comprising a knuckle arm extending upward from a knuckle.
2. Description of the Related Art
Strut type and double wishbone type wheel suspension systems are most commonly used in automobiles as the front wheel suspension systems. Strut type wheel suspension systems are simple in structure, and are therefore relatively inexpensive. The knuckle carrying a wheel is substantially rigidly attached to an outer tube or the lower end of a tubular damper. When the wheel is required to be steered, a steering gear is connected to a knuckle arm extending from the knuckle. In some cases, the steering gear is disposed above the axle of the wheel. In such a case, if the line of force transmission from the tie rod to the knuckle arm forms a large angle with respect to the direction of the motion of the knuckle arm, the force from the steering gear cannot be efficiently transmitted to the knuckle arm. Therefore, it is desirable, in such a case, to form an upwardly extending knuckle arm so that a tie rod may extend substantially horizontally between the steering gear and the knuckle arm.
However, simply extending the knuckle arm upward may lead to the need to reinforce the knuckle arm so as to have sufficient rigidity and mechanical strength, and this may undesirably increase the size and weight of the knuckle. In a strut type wheel suspension system, because the outer tube of the damper is substantially rigidly attached to the knuckle, it is conceivable to attach the knuckle arm to an intermediate part of the outer tube of the damper. However, this requires the outer tube of the damper to be sufficiently rigid and strong so as to withstand twisting and other forces that may be applied to the damper. This will require the damper to be specially designed, and is detrimental to compact and economical design of the wheel suspension system.